This invention relates to new hydrophobic rigid polyurethanes, particularly rigid polyurethane foams.
Materials based on polyurethanes are well known. See, for example, G. Oertel, "Polyurethane", Kunststoff-Handbuch, Georg Thieme Verlag, Stuttgart/New York (1987). Cast polyurethane (hereinafter referred to as "PUR") resins, flexible PUR foams and rigid PUR foams are also well known. PUR foams are crosslinked polyurethanes. Rigid foams are mostly closed-cell materials. Flexible foams are mainly open-cell materials.
In general, rigid foams are produced by the addition of a liquid low-boiling blowing agent. The most commonly used blowing agent has been fluorotrichloromethane. (See, G. Oertel, "Polyurethane", Kunststoff-Handbuch, Georg Thieme Verlag, Stuttgart/New York (1987)). However, fluorocarbons are now regarded as environmental pollutants.
For this reason, attempts are being made to replace this class of compounds with low-boiling hydrocarbons such as n-pentane or n-hexane (See,. G. Heilig, Kunststoffe, 81, page 622 (1991)). It is well known that low-boiling hydrocarbons are highly flammable liquids. Consequently, work with low-boiling hydrocarbons often involves additional and expensive safety measures to protect against explosions.
PUR matrices are, to a certain extent, hydrophilic systems. According to the literature, --NH--CO--O-- and --NH--CO--NH-- bonds enter into a relatively strong physical interaction with the water molecules, thus enabling water to diffuse into the PUR matrix (See, for example, V. Gajewski, Proceedings of the SPI-33rd Annual Technical/Marketing Conference, page 506, Technomic Publishing Co., Inc., Pennsylvania (1990)).
The generally undesirable diffusion of water into the PUR matrix can lead to
a) reduction in hydrolytic stability, PA1 b) deterioration in the thermal and electrical insulation properties, PA1 c) deterioration in the mechanical properties, particularly dimensional stability and shrinkage behavior, and PA1 d) increased permeability to gases (e.g., CO.sub.2 and O.sub.2). PA1 n represents a number of from 2 to 4, preferably 2 or 3, and PA1 Q represents an aliphatic hydrocarbon radical containing from 2 to 18 (preferably 6 to 10) carbon atoms, a cycloaliphatic hydrocarbon radical containing from 4 to 15 (preferably 5 to 10) carbon atoms, an aromatic hydrocarbon radical containing from 6 to 15 (preferably 6 to 13) carbon atoms or an araliphatic hydrocarbon radical containing 8 to 15 (preferably 8 to 13) carbon atoms.